Telephone system



Dec. 29, 1936. H. HOVLAND 2,

TELEPHONE SYSTEM Filed March 26, 1955 2 Shets-$heet 1 m S l\ u lNVE/VTOR H. HOVLAND A T TORNEK H. HOVLAND Dec. 29, 1936.

TELEPHONE SYSTEM Filed March 26, 1935 2 Sheets-Sheet 2 gllHlr 9 Q l Nl/ENTOR H. HOVLAND A TTOR/VEV EN EN Patented Dec. 29, 1936 UNITED STATES TELEPHONE SYSTEM Henry Hovland, Williston Park, N. Y., assignor Application March 26,

Claims.

This invention relates to telephone systems and particularly to those in which conversational connections are established wholly or in part by automatic switches.

The objects are to simplify and improve the releasing operations of established connections; to enable a distinction to be made between different classes of calls for certain purposes while preserving the same release conditions; and to otherwise improve such systems.

Systems have been devised heretofore in which the immediate release of all switches of the connection takes place when the calling subscriber replaces his receiver, and in which release of the final or connector switch is effected at the end of a measured interval following the replacement of the called subscribers receiver, provided the calling party is slow in hanging up his receiver. Moreover, it is common practice to employ the relay of the connector that responds to the called subscribers switchhook not only for the purpose of controlling the release circuits but also to effect a reversal in the direction of current flow in the established connection for supervision or for message register operation.

A feature of the present invention is an improvement in these prior systems which consists in providing a timing mechanism which effects the release of the connector switch at the end of an interval following the replacement of the called subscribcrs receiver and in providing an operating circuit for said mechanism which is controlled by the bridge relay, which energizes either fully or partially at the time the connection is completed and releases when the called party disconnects. This bridge relay operates fully when the call is for a subscribers line and the called party answers, and by operating fully 49 it reverses current in the usual Way for message register or supervisory purposes. However, if the call is for a line that is connected to the intercept position, the operator in answering causes the partial operation of the bridge relay, thus avoiding a current reversal and the consequent operation of the calling subscribers register. In this way the release mechanism is effective on either type of call, but such calls are distinguished from each other for the purpose of supervision or registration.

The foregoing and other features of the invention will be described more fully in the following detailed specification, which should betaken in conjunction with the accompanying drawings, and also in the appended claims.

1935, Serial No. 13,071

Referring to the drawings, Fig. 1 shows abbreviated diagrammatic representations of asubscribers telephone IM and dial I02, a line finder LF, and first and second selectors, SI

and S2, all of the usual type found in step-by- 1 step ofiices'. There are also shown in detail a connector switch C and a timing and alarm circuit A common to a number of connectors, the function of said mechanism. being to effect the release of connector C and the preceding switches of the established connection. At the right of Fig. l are shown connector terminals associated with conductors I09, I01, I88, I09, Hi3 and Hi leading to Fig. 2. To these terminals connector brushes H2, H3 and H4 have access.

In Fig. 2 there are shown two subscribers lines 2% and 2H, an intercepting operators cord.

circuit IC, which is adapted to answer intercepted calls and to complete these calls when required, and also a part of a cross-connecting frame 2M.

.Fig. 3 is: schematic of the switch train illustrating the release magnets of the respective switches.

Assume that it is desired to discontinue service on the line of station 241, and that it is necessary that incoming calls for this station be directed to an intercepting operator. For normal service the conductors 258 and ZIS of line 2!! are connected at frame 214 to conductors H39 and I it, which lead to the terminals of connector C. The line is changed to intercept service by cross-connecting conductors I09 and Hi) to conductors 2H2 and 2l3 by means of jumpers: H5 and 2H3, respectively, at the same' time opening connection with conductors 2H3 and 2&9. At the left of Fig. 2 is shown another subscribers station 203, withdial 204, which is associated with line conductors I06, I01 and H18 of Fig. 1. i For descriptive purposes it is assumed that the subscribers line 203 is connected for regular, non-intercepted service. Its frame connections and line circuit are of the usual type found in step-by-step dial offices and are omitted here, the omissions being indicated by the dotted lines.

The finder LF and selectors SI and S2 may be of any suitable type, such as the Strowger switch,

the operation and release of which are well,

known.

A detailed description of the operation of the system will now be given, first in connection with a call routed to station 203, for regular nonintercepted service, and secondly for a call to the intercepting operator who answers with the intercepting cord IC.

Let it be assumed that the subscriber of line I 0! desires to establish a connection with the;

winding of relay I03, lower inner normally closed,

contacts of relay I04, ring contacts of selectors SI, S2, and line finder LF, thence over line conductor H5 and through subscribers telephone [0| and dial I02, over conductor H6 and through tip contacts of line finder LF, and selectors Si and S2, upper normally closed contacts of relay I04 and upper winding of relay I03 to ground. Relay I03 operates and operates relay III through a circuit traceable from battery through the winding ofrelay II'I, break contacts of release magnet IIB to ground on the operated contacts of relay I03. Relay II! in operating connects ground on its lower contacts to the sleeve. contacts of selectors SI, S2 and line finder LF, thereby holding in the operated position the selectors and line finder and guarding connector C from other hunting selector circuits. On the first break of the contacts of dial I22 for the purpose of dialing the tens digits of the called number, relay I03 releases and closes a circuit from battery through the windings of vertical magnet I20 and relay IE9, upper normally closed contacts of the vertical-off-normal contact assembly I2I, upper inner operated front contacts of relay H1 to ground on back contacts of relay I03. Relay II! is slow to release and does not release during the momentary open periods of the front contacts of relay I03, while responding to the pulses of dial I02. Relay H9 and vertical magnet I20 are operated through the circuit hereinbcfore traced. As soon as the shaft of the connector switch is moved from its normal position on the first vertical step, the vertical-offnormal springs I2I operate and transfer the: operating circuit for relay H9 to vertical magnet I20 from conductors I22 and I23, thereby placing the windings of relay I I9 and vertical magnet I20 in series with the operated make contacts of relay I I9. This transfer from conductor I22 to I23 is made without interrupting the circuit, since the three upper springs of combination I2! are of the make-before-break type. After the contacts of dial I02 are closed again after the first break, relay I23 reoperates and again closes the circuit through the winding of relay II'I, before this relay has had time to release, as hereinbefore explained. On the next open period of dial I02, relay I03 again releases and transmits a second ground pulse, through the circuit ofrelay H9 and vertical magnet I20. Relay IE9 is slow to release and remains locked up over the open periods of the back contacts'of relay I03. The second ground pulse aforesaid causes the shaft of the switch to take another step upward. This action continues until all required pulses for the tens digits are transmitted by dial I02 and connector brushes II 2, H3 and H0 have reached the level containing the terminals of the line being called.

After the tens digit. has been dialed and dial I02 is restored to normal relay I83 remains operated, relay H0 releases, and the Winding of vertical magnet I20 is deenergized. When relay II9 releases a circuit is closed through rotary magnet I24 for rotary stepping. This circuit may be traced from battery through the winding of rotary magnet I24, normally closed springs I26 and I2! of relay I28 to junction point I29, from battery through the winding of relay I251 to said junction point I29, thence through the upper normally closed contacts of relay I30, back contacts of relay IIQ, over conductor I23, through upper operated contacts of combination I2I to the upper inner front contacts of relay Ill. On the first break of dial I22 for dialing the units digits of the called number, i. e., for rotary stepping, relay I03 releases and transmits a ground impulse through the upper, inner, operated front contacts of relay III and the rotary stepping circuit just traced. Relay II'I remains operated during dial pulses, as in the case of vertical stepping. In response to said first ground impulse rotary magnet I22 will operate and cause the switch. to rotate one step in the horizontal direction and relay I25 will operate and short circuit the upper contacts of relay I30, which were included in the original operating circuit. Subsequent dial pulses cause rotary magnet I24 to step the switch around until the line 203 of the called subscriber is reached.

Before connecting ringing current to this line a test is made to determine whether the line is busy or idle. If busy, ground will be found on the sleeve terminal connected to conductor I08, and will cause the operation of test relay I30 from battery through its winding, normally closed contacts I 3! and I32 of relay I28, lower operated make contacts of slow release relay I25, conductor M l, to ground on sleeve conductor I08 through brush H4. Relay I30 in operating opens through its upper break contacts the original circuit for rotary magnet I24 and when slow-release relay I25 finally releases after rotary pulsing is completed further rotary srtepping is stopped. Relay I253 in operating connects to ring conductor I34 from the secondary winding of transformerl33, through its lower outer make contacts, a potential of audible frequency, interrupted by the usual busy-back interrupter (not shown) and which indicates to the calling subscriber it! that the called line is busy. Relay ISQ is locked up through a circuit traced from battery through the winding of relay I 30, contacts I3! and I32 of relay I28, lower inner back contacts of relay I25, lower inner operated make contacts of relay I30 to ground on sleeve conductor I35. Under this condition the calling subscriber will disconnect, causing the release of relays I83 and H1, thereby closing a circuit from battery through the winding of release magnet Ht lower operated contacts of VON combination I2I, normally closed contacts I36 and I3! of relay I23, through back contacts of relays II] and I 03 to ground. Release magnet II 8 is energized and causes the restoration of the connector switch, including VON springs I2! to normal. Relay I 32, which was locked to ground on sleeve conductor I35, releases since ground was removed by the opening of the lower make contacts of relay II! when this relay released. The removal of ground from conductor I35 causes in the well-known manner the energization of release magnets 300, 30L 302 of the preceding switches and the consequent release of these switches.

Let it be assumed now that the line 203 of the called subscriber is found idle. Under this condition battery will be found by sleeve brush H4 on the terminal connected to sleeve conductor I08. This conductor is connected through the winding of cut-off relay 222. Under this condition relay I39 will not operate as hereinbeiore described when the line 203 was found busy, since now a battery potential is connected to both winding terminals of relay I30. After relay I25 has released upon the completion of rotary stepping, a circuit is closed for the operation of relay I28, which may be traced from aforesaid battery connection on brush Il l, through lower outer normally-closed contacts of relay I25, lower winding of relay I28, lower normally-closed contacts of relay I30, to ground on sleeve conductor I35. Relay I28 in operating looks through its upper winding and upper inner make contacts to ground on the upper outer operated make contacts of relay 1. In operating relay I28 also connects tip conductor I38, through its upper, outer contacts to ground on the upper back contacts of relay I39; opens the circuit of the winding of relay I30, by opening its contacts I3! and I32; connects ground from pick-up interrupter M0, through its lowerinner make contacts, inner normally closed contacts of relay I ll, lower inner normally closed contacts of relay I39 to battery through the winding of relay I II. Relay I l! operates and looks through its inner make contacts to ground on the lower operated contacts of relay II'I. Relay I28 in operating also disconnects the winding of rotary magnet I24 by opening its contacts I26 and I21; connects ring conductor I l-2 to conductor I43 through the contacts of springs connected thereto and joins sleeve conductor I35 to sleeve conductor I44, thereby grounding said conductor I44, operating cut-off relay 222, and guarding the terminals of the line of subscriber 203 from seizure by another connector.

When relay It! operates it closes a circuit for ringing the station 2E3. This circuit is traced from source of ringing current I41, which may comprise an alternating-current generator connected in series with battery, through lower operated make contacts of relay MI, lower winding of relay I39, lower outer normally closed contacts of relay I39, over conductor Hi3, associated operated contacts of relay I28, over conductor I42, through connector brush H3 and associated contacts, over line of subscriber 2E3, connector brush H2 and associated contacts, conductor I38, upper outer operated contacts of relay I28, to ground on the upper outer back contacts of relay I39. The ringer (not shown) of station 263 is now actuated, but relay I39 does not operate on the ringing current through its lower winding until subscriber 203 answers by removing his receiver from the switchhook, thereby connecting a low impedance bridge across the line. Ringing tone is sent back to the calling subscriber through condenser Hi8. Relay I39 is adjusted so that in operating a locking circuit is closed from battery through its upper winding and upper inner make contacts to ground on the upper outer contacts of relay II'I before the circuit through its lower winding is broken at either its upper or lower outer break contacts. If the called subscriber should remove his receiver from the switchhook before relay MI operates in response to pick-up interrupter I40, then relay I39 operates from the battery on the lower back contacts of relay MI. The operation of relay I39 accordingly, either disconnects ringing current or the aforesaid battery on the lower contacts of relay 1 H.

Relay I39 also completes the conversational circuit between the calling and called subscribers, by closing through the tip conductors on its upper outer make contacts, and the ring conductors on its lower outer make contacts, and opens the locking circuit for relay I4I which releases. Relay I39 in operating also completes the operating circuit for relay I64, which may be traced from battery through the upper winding of relay Hi4, over the tip conductors of connector C and the line of station 283, through station 2123 including dial 2%, ring conductors of the line and of connector C to ground through the lower winding of relay I04. Relay I86 in operating reverses the direction of current over the line of calling station IEII, thereby causing the operation of an associated line message register (not shown) in the well-known manner. After aforesaid reversal, battery through the lower winding of relay I83 is connected by the upper operated make contacts of relay ISM to the tip conductor, and ground through the upper winding of relay IM by the lower make contacts of relay I04 to the ring conductor.

At the end of the conversation, when the calling subscriber disconnects, relays I03 and I I! release, removing ground from the upper locking windings of relays I39 and I28, which release. The release of relay I28 closes a circuit for operating release magnet H8, which may be traced from battery through the winding of magnet II8, lower make contacts of VON combination I2I, contacts I36 and Ilil of relay I28, to ground through upper back contacts of relays Ill and IE3. The operation of release magnet H8 restores the connector switch to normal in the well-known manner. Also the removal of ground from conductor I35 causes the operation of release magnets 30G, 3M, and 302 and the immediate release of the preceding switches L71", SI, and S2.

A description will now be given of that feature of the system whereby the called subscriber by hanging up his receiver is enabled to effect a timed release of the connector C and all the other switches of the connection, assuming that the calling subscriber fails to disconnect promptly. When called subscriber at station 203 disconnects, relay I64 releases, restoring the original direction of current flow, but relay I93 and relay II'I remain operated and also relays I28 and I39. A circuit is now closed from battery through the winding of release magnet H8, lower operated contacts of VON combination IZI, lower outer break contacts of relay Ill-i, lower middle operated contacts of relay I39, resistance I69, winding and normally closed contacts of relay I5I to the armature of relay I52. The interrupter I53 is arranged to connect ground to the winding of relay I55 for two minutes and then to disconnect said ground for two minutes. When relay I5t operates through an obvious circuit in response to the closure of said interrupter contacts, relay I52 also operates through an obvious circuit. On the next opening of the inter-.

rupter contacts, relay 552 releases immediately, but relay I52 being slow to release holds up momentarily, and a circuit is closed for operating relay I5I, which is traced from ground on the back contacts of relay I5 1, through operated contacts of relay I52 and thence through the hereinbefore traced circuit to battery on the winding of release magnet IE8. Relay I5I locks to ground on its upper make contacts, but release magnet II8 does not receive sufiicient current in this circuit to open its contacts. On the next closure of interrupter I53 relay I54 re-, operates and closes a circuit for operating relay I55, which circuit may be traced from ground on the lower contacts of relay I 54, through lower operated; contacts of relay ml and through lower winding of relay I55 to battery. Relay I55 now operates and looks through its low-resistance upper winding to the release magnet circuit, hereinbefore traced. This causes a shunting down and release of relay 55!. The low resistance ground applied through the upper winding of relay I55 now permits sufficient current to flow through release magnet M8 to open the contacts of said magnet, thereby releasing relay H1. However, magnet H8 does not energize sufliciently to release connector C. The release of relay I I? removes ground on its lower contacts from sleeve conductor I35, which causes the release of the preceding switches and relay I03. Relay Ill in releasing also causes the release of relays I33 and I2l by removing the hold-- ing ground from the upper windings of these relays. When relay I28 releases a circuit is closed, for fully operating release magnet II8 which may be traced from battery through the winding of release magnet H8, lower operated contacts of VON combination 923, contacts ltd and I3? of relay 528, upper back contacts of relays Ill and M33 toground. The connector switch, including the VON springs Hi and all associated apparatus is now restored to normal. When the circuit through release magnet H8 is opened relay I 55 is unlocked and releases. If, however, due to some trouble condition the connector fails to release, as hereinbefore described, provision is made for indicating the presence of this trouble condition. When relay I55 operated it also operated relay I58 through an obvious circuit. Relay I58 in operating closes a circuit to battery through lamp m5 and a pick-up circuit (not shown), which is arranged so that, if relay I56 remains operated for a certain predetermined interval, lamp ltfi is lighted and remains lighted until the trouble condition is manually removed and relay I55 and I513 release.

The operation of the system has been described for a regular, non-intercepted call between subscribers. The system will now be described in its operation for an intercepted call. Assume for this purpose that the calling subscriber at station Elli wishes to be connected to subscribers line 2H, whose telephone, as hereinbefore stated, has been removed from service by disconnecting conductors I69 and II!) on frame 2M from line conductors 2E8, and ZIQ, and by cross-connecting said conductors Hit and H3 by jumpers 2I5 and 2% to conductors 2I2 and Zit leading to jack 25! at an intercepting operators position. Also the line relay 22! is disconnected, and the sleeve conductor iIl is disconnected from relay 229 and connected by jumper 28l to sleeve conductor 282 of trunk 2i2-2i3. Let it be further assumed that a connection has been made in the usual manner by connector brushes H2, H3, H4, with terminals connected to conductors H39, lit and Ill of line 267. The description of the operation for establishing the connection with conductors IE6, ml, and IE3 is sufiicient to explain the connection with conductors M9, M9 and iii. When the connector switch engages the terminals of line I59, III], 1H, relay 28 operates in the manner already described, the current for operating the relay being furnished in this instance from battery through the resistance 29I and thence over conductors 282, 28I and III through the winding of relay I28 as previously traced. Ringing current transmitted over conductors 2I2 and 2I3 causes the operation of a line signal (not shown) associated with jack 20I. The intercepting operator in response inserts plug 223 into jack 2UI, thereby closing a circuit for operating relay 224, over a circuit that may be traced from battery on the inner back contacts of relay 225, through the winding of relay 224, lower back contacts of relay 228, ring conductors of plug 223, and jack 20I, to a ground (not shown) on the ring conductor of trunk 2 I2 2 I3. Relay 224 in operating, operates relay 22'! through a circuit from ground on the contacts of relay 224 through the right-hand inner back contacts of relay 221, resistance 228 and battery on the right-hand outer back contacts of relay 225. Relay 221 in operating connects a ground to the ring conductor through resistance 229, thereby-operating relay I 39 of the connector circuit through its lower winding in the manner described hereinbefore in connection with the call to station 253. The operation of relay I39 trips the ringing. The circuit for operating relay I39 may be traced from ground on the upper back contacts of relay 226, relay 221, resistance 229, lower back contacts of relay 225, ring conductors of plug 223 and jack 2M, conductor 2I3, jumper 2I6, conductors 2H] and IIll, brush II3, conductors I42 and I43 and associated operated contacts of relay I28, lower outside back contacts and winding of relay I39, outer operated front contacts of relay MI, and source of ringing current I41 to ground. Relay 227 in operating locks to ground on the sleeve of jack 2M, through its right-hand inner make contacts and operates relay 230 through an obvious circuit. Relay 230 in operating operates through an obvious circuit relay 225, which disconnects ground from its upper back contacts and the winding of relay 224 from its lower back contacts. Relay 225 releases. Relay 226 in operating, connects through, with its lower front contacts the ring conductors of cord circuit IC and with its upper front contacts connects ground to conductor 23I through the upper contacts of key 238. Key 238 is a flashing key for use with calls from an operator. When relay 226 operated, it connected through the lower back contacts of key 238 a bridge across the tip and ring conductors of cord circuit IC, said bridge including retardation coil 235 and relays 232 and 236 all in series. Polarized relay 236 is used for toll calls. In multiple with the series connection of the windings of relays 232 and 236 is a resistance 231. Relay 232 operates in series with the windings of relay I04 over the tip and ring conductors of cord circuit IC, through the operated contacts of relay 226, thence over tip and ring conductors of the connector C, which are closed through by operated contacts on relays I23 and I39. Relay 232 in operating disconnects the windings of relay 225 from the righthand outer contacts of relay 23S. Consequently relay 225 does not operate when ground is connected to conductor 23I by the aforesaid operation of relay 226. Relay 235 does not 0perate in series with relay 232 as the current flow through its winding is in the direction opposing operation. Because of the resistance in the circuit traced, relay I04 operates only partially in accordance with a feature of this invention, sufficiently to open its lower outer break contacts,

righthand outer make contacts of but not enough to operate its other contacts.

Accordingly there is no reversal of current over the tip and ring conductors extending towards the station of calling subscriber Hll, thereby avoiding the operation of the line register, which, of course, should not operate on this call to an intercepting operator. The operation of aforesaid lower break contacts of relay 1M opens the hereinbefore described timed release circuit that was momentarily closed through the lower middle make contacts of relay I39.

The intercepting operator now operates the listening key 239 and thereby connects the operators telephone (not shown) to the tip and ring conductors of the cord circuit IC. The operator converses with the calling subscriber iii! and if desired the connection may be extended over another line (not shown) which terminates on jack 282. If there is a multiple of jack 2632 the usual busy test is made through the tip conductor of plug 242 and the upper back contacts of relay 2M. serted into jack 222 and relay 2 operates through an obvious circuit over the sleeve conductors of plug 2% and jack 2B2. Relay 2' in operating connects the windings of a supervisory relay 242 to the tip and ring conductors of plug 240 and connects through normally closed contacts of key 2 33 said tip and ring conductors to the corresponding conductors of the answering end of cord circuit IC. The conversational connection with the called line is now completed through condensers 2M and 225. By operating key 223, the intercepting operator can split the connection and talk only on the line of jack 222. Relay 2 5! in operating closes a circuit from battery on its outer lower contacts through the contacts of relay 2-22 to ground through supervisory lamp 225, which lights. When the call is answered relay 222 operates, extinguishing lamp 246.

The operation of the system will now be described for the various conditions of release after the call to the intercepting operator has been established as hereinbefore described. When the party of the line connected to jack 202 disconnects, relay 222 releases and closes again the circuit of lamp 226 which lights as a disconnect signal. Plug 226i is now withdrawn from jack 202. If the calling subscriber lfil, disconnects, the connector circuit C is restored to normal as hereinbefore described in connection with the call between subscribers lill and 203. The circuit through relay 232 is accordingly opened, and this relay releases closing a circuit for operating relay 225. This circuit may be traced from battery through the winding of relay 225, contacts of relay 232, outer break contacts of relay 233 to ground on conductor 23!. Relay 225 in operating closes an obvious circuit through supervisory lamp 241 which lights. The operation of relay 225, disconnects battery on its outer break contacts from the winding of relay 227, which releases thereby causing the release of relays 236 and 226. Relay 225 in operating operates relay 234 through a circuit from battery on its inner make contacts through the winding of relay 234 to ground on the sleeve conductor. In operating relay 234 connects ground to conductor 23!, to replace the ground removed by the release of relay 226. In response to the lighting of the lamp 221! the intercepting operator now removes plug 223 from jack thereby removing ground from the sleeve conductor of plug 223,

If the line is found idle plug 260 is inreleasing relays 234 and 225. All apparatus of 'Fig. 1 and Fig. 2 is now restored to normal.

The operation for the release of the connection has been described in the preceding paragraph for the condition existing when the calling subscriber Mil disconnects promptly at the end of the conversational period. Assume now, however, that said calling subscriber IQI delays in hanging up his receiver. Accordingly, the intercepting operator by removing plug 223 from jack 29! may eifect the release of the connector circuit C in the manner hereinbefore explained in connection with the call between stations IUI and 223. When plug 223 is removed from jack 20! the circuit through the partially operated relay )4 is opened. Relay H34 releases and closes its lower outer break contacts thereby connecting the winding of release magnet M8 to alarm circuit A which new functions in the manner hereinbeio-re described to cause the timed release of the connector circuit C.

It will be noted that the circuit from the connector C to the timing device A by way of resistance M9 is closed by the operation of ringing-trip relay I39 as soon as a called subscriber or the intercept operator answers. However, this circuit is immediately opened at the lower contact of relay EM, which also operates either when the subscriber or the operator answers.

But when the called subscriber or the intercept operator disconnects, after having answered and operated relay E39, relay Hi l releases its lower contact, and the timing circuit becomes eifective. As has been explained, the resistance of this circuit is reduced after a measured interval to cause release of all selectors, following which the connector C is released.

What is claimed is:

1. In a telephone system, an automatic switch, circuits of diiTerent classes accessible to said switch, means including said switch for establishing a connection to a circuit of any one of said classes, a timing mechanism for controlling the release of said switch, a relay for said switch operable over a circuit of one of said classes for sending a signal over the established connection and operable over a circuit of another of said classes without sending said signal over the established connection, and a circuit for said timing mechanism controlled Q on each operation of said relay.

2. In a telephone system, a called line of one class, a called line of a second class, means including an automatic switch for extending a connection to either of said lines, release means for said switch, a relay for said switch operable when connection is extended to one of said called lines for reversing the direction of current in the established connection, said relay being operable when connection is extended to the other of said called lines Without reversing the direction of current, and a circuit for said release means controlled by said relay when connection is extended to either of said lines.

3. In a telephone system, a called subscribers line, an operators position, means including an automatic switch for extending a connection to said line or to said position, a release magnet for said switch, timing mechanism, a source of current for the extended connection, a relay operable when the subscriber of said line answers for reversing the direction of current from said source, said relay being partially operable Without reversing the current direction when extended connection, and a circuit for said release magnet controlled by said timing mechanism, said circuit being opened by said relay on connections extended either to said subscribers line or to said operators position.

4. In a telephone system an automatic switch, circuits of two difierent classes accessible to said switch, means including said switch for extending a connection to a circuit of either of said classes, a timing mechanism for controlling the release of. said switch, a relay for said switch having contacts for supplying current to the extended connection, said relay being energized over a circuit of one of said classes for operating said contacts to send a signal over the extended connection and energized over a circuit of the other class without operating said contacts, other contacts for said relay operated on each energization thereof, and a circuit for said timing mechanism controlled by said other contacts.

5. In a telephone system, a called subscriber's line, an operators position, means including an automatic switch for extending a connection to said line or to said position, a cord circuit at said position for answering calls extended thereto, a release magnet for said switch, timing mechanism, a source of current for the extended connection, a relay associated with said switch, an operating circuit including the subscribers line for operating said relay when the subscriber answers, said relay in operating serving to reverse the direction of the current from said source, an operating circuit including the operators cord for energizing said relay when the operator responds to a call extended thereto, resistance means in said last mentioned circuit for preventing said relay from operating fully, and a circuit for said release magnet controlled by said timing mechanism, said circuit being opened by said relay on connections extended either to said subscribers line or to said operators position.

HENRY HOVLAND. 

